In the field of eye protection disclosure of the above '748 application provides for blocking of direct transmission of light to a person to protect the eyes from intense radiation or the like. Such blocking is effected by causing a scattering of light due to index of refraction considerations brought about automatically in response to the input of a prescribed radiation to the device. Since the light/radiation is scattered, the intensity thereof is significantly reduced. After the intense radiation condition is alleviated, the device can be re-set to transmit light and images carried thereby by applying appropriate electrical and/or temperature inputs to the device. The device relies on smectic liquid crystal material and Kerr effect occurring therein to defocus light with respect to curved surfaces within which the liquid crystal is contained or with respect to which the liquid crystal is positioned. The device is generally insensitive to wavelength.
Scattering of light in response to a mismatch of index of refraction between liquid crystal material and a containment medium is disclosed in two first-mentioned patents above. Transmission of such light will occur in response to a prescribed input, such as an electric field or a magnetic field. The devices disclosed in such patents utilize nematic curvilinearly aligned phase liquid, which preferably has positive dielectric anisotropy and an ordinary index of refraction that is matched to the containment medium so as to minimize scattering when the liquid crystal is aligned with respect to an electric field, for example. The liquid crystal also has an extraordinary index of refraction that is different from the index of refraction of the containment medium; therefore, in the absence of an electric field, for example, the liquid crystal, which assumes a somewhat curvilinear alignment, and the containment medium tend to scatter light.
The relationships of certain optical components for affecting light, particularly polarized light, is described, for example, in Jenkins and White, FUNDAMENTALS OF OPTICS, McGraw-Hill Book Company, New York, 1957. For example, at Chapter 27 of such text, the interference of polarized light is described. Polarized light and use of various optical components with polarized light also are described elsewhere in such text. The entire disclosure of such text is incorporated herein by reference.
A liquid crystal device for phase modulating polarized light is disclosed in U.S. Pat. Nos. 4,385,806 4,436,376, 4,540,243, and Re. 32,521. The disclosures of such patents hereby are incorporated by reference. In such device linearly polarized light is phase-modulated as such light passes through a liquid crystal cell to which a modulated electrical carrier wave signal is applied as an electrical potential to develop an electric field across the liquid crystal material affecting alignment of the liquid crystal structure therein. The light which is transmitted through the liquid crystal cell is phase modulated as a function of the modulated electrical carrier wave signal. More specifically, the liquid crystal cell effectively separates the incident linearly polarized light into the quadrature components, i.e., the ordinary and extraordinary rays, thereof, and effects a retardation of one ray or component relative to the other as the light is transmitted through the cell. The amount of retardation, i.e., the effective optical thickness of the liquid crystal cell, is a function of the modulated electrical carrier wave signal. The liquid crystal cell disclosed in such patents utilizes a so-called surface mode switching technique which is fast acting, e.g., for example providing switching response times of as little as 10 to 100 microseconds.
In the variable rotator patent application mentioned above, an apparatus for rotating polarization of polarized light, includes a source of linearly polarized input light or a means to effect linear polarization of input light, a variable retarder that retards the phase of one quadrature component of such linearly polarized input light an amount relative to the phase of the other quadrature component, and an analyzer that converts the quadrature components from the variable retarder to linearly polarized light that has a plane of polarization which is a function of the amount of such phase retardation. The variable retarder is a liquid crystal cell that operates according to surface mode alignment and switching characteristics in response to electric field input to alter the relative retardation or phase separation of the ordinary and extraordinary ray components of incident light. Such liquid crystal cell is disclosed in the aforementioned U.S. patents.
In the notch filter patent application mentioned above, there is disclosed an apparatus for filtering a wavelength of light, including a variable polarization rotator for supplying input light as polarized light at a prescribed angle of polarization, a variable dispersion device for rotating the angle or plane of polarization of such input light an amount that is a function of the wavelength of such input light, and an analyzer for blocking transmission of that light which is output by said variable dispersion device and has a plane or angle of polarization which is crossed relative to the axis of polarization of such analyzer. The apparatus for rotating polarization is that of the variable rotator patent. An example of a wavelength dependent optical dispersion device is a liquid crystal cell with parallel plate walls, e.g., of glass, with a quantity of cholesteric liquid crystal between the walls.